Ground freezing method and apparatus with geothermal gradient compensation

ABSTRACT

A ground freezing method and apparatus compensates for geothermal gradients by supplying more refrigerant to deeper parts of the earth. One or more metal freeze pipes are installed in a bore and equipped with one or more feed pipes. The feed pipes extend to different depths with the longer feed pipes being larger to supply more refrigerant to greater depths and achieve uniform top to bottom ground freezing despite the effects of geothermal gradients.

FIELD OF THE INVENTION

This invention relates generally to artificial ground freezing and is directed more specifically to improved ground freezing techniques that compensate for geothermal gradients.

BACKGROUND OF THE INVENTION

Artificial ground freezing is used to freeze selected areas of the ground for a variety of different purposes, including temporary earth support for excavations, ground water containment and control, confinement of hazardous materials in the ground, and the creation of impermeable zones for hydrocarbon or mineral extraction or processing. Typically, spaced apart bores are drilled and equipped with metal freeze pipes installed along a barrier line or around a perimeter of a proposed excavation or other site. Feed pipes extend into the freeze pipes and direct a refrigerant to the base areas of the bores. The refrigerant then flows upwardly in the freeze pipes and freezes the earth around them. The refrigerant is collected and cooled again, and then circulated through other freeze pipes. Eventually, a frozen subterranean barrier is formed continuously between the adjacent freeze pipes.

In applications requiring the ground to be frozen to a substantial depth, geothermal gradients can lead to a lack of uniformity in the freezing of the ground from top to bottom. Because the deeper areas are warmer due to the presence of geothermal gradients, they require a longer time to freeze, a problem that increases with increasing bore depth. As a result, the shallower areas freeze more quickly, and the subterranean frozen barrier that is formed is uneven. In some applications, this can be a significant problem that detracts from the ability of the barrier to function as intended.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus involving ground freezing techniques that compensate for geothermal gradients. Consequently, subterranean barrier walls are formed more evenly and uniformly from top to bottom even when the bores are relatively deep.

In accordance with the invention, a bore that is drilled in the ground can be equipped with one or more freeze pipes. In the case of a bore with a single freeze pipe, at least two separate feed pipes are provided extending to different depths. The longer feed pipe is larger in diameter so that more refrigerant is supplied to the bottom area of the well where the earth is warmer due to geothermal gradients. By properly sizing the pipes based on the bore size and depth, the earth around the freeze pipe can be frozen in a relatively uniform manner from bottom to top. The refrigerant from the freeze pipe can be collected and recirculated through other bores. The freeze pipes and feed pipes can be of uniform diameter, or they can be dual diameter pipes with transition areas at a depth near the end of the shorter feed pipe.

In the case of a bore having plural freeze pipes, the freeze pipes extend to different depths with each having a separate feed pipe. The deeper freeze pipe receives more refrigerant than the shorter freeze pipe, as can be achieved by proper sizing of the pipes based on the bore depth and diameter.

Using the techniques of the present invention, the frozen subterranean barrier is formed more uniformly than is achieved by a single feed pipe in a single freeze pipe, and compensation is made for geothermal gradients in a way that results in an economically formed subterranean barrier that exhibits improved functionality.

Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.

DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIG. 1 is a diagrammatic view of a ground freezing pipe arrangement constructed according to one embodiment of the present invention;

FIG. 2 is a diagrammatic view of a ground freezing pipe arrangement constructed according to a second embodiment of the invention; and

FIG. 3 is a diagrammatic view of a ground freezing pipe arrangement constructed according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in more detail and initially to FIG. 1, the present invention is directed to a method and apparatus for ground freezing which involves drilling of a bore 10 downwardly from the surface 12 into the ground or earth 14. A freeze pipe 16 which may be constructed of steel or another metal is installed in the bore 10 generally in contact with the sidewall of the bore. The freeze pipe 16 may extend to the bottom or base 18 of the bore 10.

Extending side by side within the freeze pipe 16 are a pair of feed pipes 20 and 22. At their upper ends, pipes 20 and 22 are connected by a Y fitting 24 with a common supply pipe 26. Pipe 20 is substantially longer than pipe 22 and extends downwardly from the Y fitting 24 to an open lower end 28 which is spaced slightly above the bottom of the freeze pipe 16 near the base 18 of the bore. Pipe 22 has an open lower end 30 which is located well above end 28 of pipe 20 at a mid-depth location within the freeze pipe 16. The diameter of pipe 20 is greater than the diameter of pipe 22. The feed pipes 20 and 22 may be constructed of any suitable material such as high density polyethylene (HDPE).

By way of example, pipe 22 may be a one inch diameter pipe extending to a depth within the bore of 1000 feet. The other pipe 20 may be a two inch diameter pipe extending to a depth of 1750 feet.

A suitable refrigerant is supplied to the feed pipes 20 and 22 through a hose 32 extending from a suitable refrigeration source (not shown). The hose 32 connects through a valve 34 with the supply pipe 26 at a location above the ground surface 12. The freeze pipe 16 is provided with a discharge pipe 36 at an above ground location. The discharge pipe 36 is equipped with a valve 38 that connects with a discharge hose 40. The discharge hose 40 may connect with a refrigeration plant (not shown) which cools the refrigerant and then recirculates it through another ground freezing bore equipped with a pipe arrangement similar to that of FIG. 1 or some other ground freezing pipe arrangement.

In use, refrigerant is pumped from the refrigeration source (not shown) through hose 32, valve 34 and supply pipe 26 to the feed pipes 20 and 22. The refrigerant that is pumped downwardly through feed pipe 20 is discharged in the bottom area of the bore 10 which is considerably warmer than upper areas of the bore due to geothermal gradients. The refrigerant that discharges from feed pipe 20 through its open lower end 28 passes upwardly within the freeze pipe 16 as indicated by the directional arrows 42, thus freezing the earth around the entire depth of bore 10. Similarly, the refrigerant that discharges through the open lower end 30 of feed pipe 22 passes upwardly within freeze pipe 16 as indicated by the directional arrows 44. This provides a freezing effect to the earth 14 around the upper portion of bore 10. The earth 14 around bore 10 is frozen over time until a solid frozen barrier is formed from the freeze pipe 16 to adjacent freeze pipes in a manner known in the art.

The provision of the two feed pipes 20 and 22, with pipe 20 extending to a deeper location within the bore and having a greater diameter than pipe 22, results in more refrigerant being provided to the lower portion of the bore where the earth is warmer due to geothermal gradients. As a result, the warmer lower portion of the bore freezes approximately as quickly as the cooler upper portion of the bore so that the earth 14 is frozen uniformly from top to bottom around the bore 10.

FIG. 2 depicts an alternative embodiment of the invention in which a bore 110 is drilled downwardly from the surface 112 of the ground or earth 114. The bore 110 is provided with a pair of side by side freeze pipes 116 and 117 which are preferably constructed of steel or another metal. Freeze pipe 116 extends to the base 118 of the bore 110, while the other freeze pipe 117 extends downwardly into the bore to a mid-depth level well above the base 118.

A feed pipe 120 extends centrally within freeze pipe 116 and has a lower open end 128 located a short distance above the bottom of freeze pipe 116. Another feed pipe 122 extends centrally within the other freeze pipe 117 and terminates in an open lower end 130 located a short distance above the bottom of freeze pipe 117. The feed pipes 120 and 122 may be constructed of any suitable material such as HDPE.

A supply of refrigerant is delivered through a hose 132 and valve 134 to the top end of feed pipe 120. The shorter feed pipe 122 similarly receives refrigerant through a hose 133 and valve 135. A discharge pipe 136 is connected with the side of freeze pipe 116 at an above ground location. The discharge pipe 136 connects with a valve 138 which in turn connects with a discharge hose 140. A similar supply pipe 137 connects with the top end portion of freeze pipe 117 at an above ground location. The discharge pipe 137 is equipped with a valve 139 which in turn connects with a discharge hose 141. The discharge hoses 140 and 141 may direct the refrigerant to be recooled and recirculated.

The longer feed pipe 120 is preferably greater in diameter than the shorter feed pipe 122. Consequently, pipe 120 delivers more refrigerant to the deeper areas of the bore 110 than is delivered by the shorter feed pipe 130.

In use, refrigerant is supplied to feed pipe 120 through hose 132 and valve 134. The refrigerant that discharges from the lower end 128 of feed pipe 120 passes upwardly within freeze pipe 116, as indicated by the directional arrows 142. As the refrigerant passes upwardly within freeze pipe 116, it provides a freezing effect to the ground surrounding the entire depth of bore 110. When the refrigerant reaches the surface, it passes through the discharge pipe 136 and valve 138 to the hose 140 which may deliver the refrigerant to a refrigeration plant (not shown) for recooling and recirculation through another bore.

Similarly, refrigerant is pumped through hose 133 and valve 135 to the other feed pipe 122. The refrigerant discharges from the lower end 130 of pipe 122 into the freeze pipe 117. The refrigerant flows upwardly within freeze pipe 117 as indicated by the directional arrows 144 and thereby provides a freezing effect to the upper portion of the bore 110 and the surrounding earth 114. The refrigerant within freeze pipe 117 passes through the discharge pipe 137 and valve 139 to hose 141 which may deliver the refrigerant to a refrigeration plant for recooling and recirculation.

Because the earth 114 is warmer at deeper locations around bore 110, the provision of a larger feed pipe 120 to provide greater amounts of refrigerant to the lower portions of the bore results in uniform freezing of the soil around the bore from bottom to top, in a manner similar to that achieved by the embodiment of FIG. 1. In the embodiment of FIG. 2, the metal freeze pipes 116 and 117 are of smaller diameter than in the case of a freeze pipe that occupies the entirety of the bore, and economies can be obtained in this regard in many applications. Also, coiled tubing and other types of piping can be used in the embodiment shown in FIG. 2.

FIG. 3 depicts still another embodiment of the invention in which a bore 210 is formed to extend downwardly from the surface 212 into the ground 214. The bore 210 may be formed as a dual diameter bore and may be equipped with a dual diameter freeze pipe 216 having an upper section 216A that is smaller in diameter than a lower section 216B which connects with the upper section by a transition section 216C situation at a mid-depth location. By way of example, section 216A may have a six inch diameter with section 216B having an eight inch diameter. The lower end of the larger section 216B is adjacent to the base 218 of the bore 210.

A pair of feed pipes 220 and 222 extend side by side in the freeze pipe 216. The feed pipes 220 and 222 may be constructed of any suitable material including HDPE. Feed pipe 220 may be a dual diameter pipe having an upper section 220A which is smaller in diameter than a lower section 220B. A transition section 220 connects the upper and lower sections 220A and 220B and may be located in the area of the freeze pipe transition section 216C. By way of example, with the feed pipe 216 having the dimensions previously set forth, section 220A may have a two inch diameter and section 220B may have a three inch diameter. Section 220B terminates in an open lower end 228 located a short distance above the bottom of the feed pipe 216.

Feed pipe 222 may be smaller in diameter than section 220A of the other feed pipe 220. For example, feed pipe 222 may have a one inch diameter. Pipe 222 is shorter than pipe 220 and terminates in an open lower end 230 which may be located in the area of the transition section 216C of the feed pipe 216, well above the end 228 of pipe 220.

The feed pipes 220 and 222 connect at their upper ends with a Y fitting 224 installed in the feed pipe 216 at a location near the ground surface 212. The upper end of the Y fitting 224 connects with a supply pipe 226 which in turn connects with a hose 232 through a valve 234. The hose 232 is supplied with refrigerant from a suitable refrigeration plant (not shown). The feed pipe 216 is provided on its side with a discharge pipe 236 which may be at an above ground location. The discharge pipe 236 is equipped with a valve 238 which connects with a discharge hose 240. The hose 240 may extend to a refrigeration plant which is used to recool the refrigerant and recirculate it to another bore.

In use, refrigerant is pumped through hose 232 and passes through the valve 234 and supply pipe 226 and fitting 224 to the feed pipes 220 and 222. The refrigerant supplied to pipe 222 discharges near the bottom of the bore 210 through the open lower end 228 of pipe 220. The refrigerant then flows upwardly within the feed pipe section 216B as indicated by the directional arrows 242. The refrigerant thus cools the lower feed pipe section 216B and the earth around the freeze pipe and bore. The refrigerant continues to flow upwardly through the smaller diameter section 216A of the feed pipe to provide cooling of the earth around the upper part of the bore Similarly, the refrigerant that is pumped into feed pipe 222 passes through its open lower end 230 and then flows upwardly within the upper freeze pipe section 216A, as indicated by the directional arrows 244. The refrigerant thus provides a freezing effect for freezing of the earth 214 surrounding the upper part of the bore 210. The refrigerant from both of the feed pipes is collected in the upper part of the freeze pipe 216 and is discharged through pipe 236, valve 238 and hose 240.

Again, by providing feed pipe section 220B with a larger diameter than feed pipe 222, more refrigerant is supplied to the lower, warmer part of the bore so that freezing is achieved in a relatively uniform manner from top to bottom.

It is thus evident that the present invention provides a method and apparatus making use of techniques that compensate for thermal gradients and overcome the effects of thermal gradients in order to achieve relatively uniform and even freezing of the earth from top to bottom of the bores. It is contemplated that the bores will be provided at spaced apart locations so that the ground that freezes between them eventually forms a continuous barrier of frozen earth.

From the foregoing it will be seen that this invention is one well adapted to attain all ends and objects hereinabove set forth together with the other advantages which are obvious and which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense. 

1. Apparatus for freezing ground adjacent to a bore, said apparatus comprising: a freeze pipe in said bore extending therein from the surface; a first feed conduit in said freeze pipe extending therein to a preselected depth and having a first diameter, said first feed conduit having an upper inlet end and a lower discharge end; a second feed conduit in said freeze pipe extending therein to a depth greater than said preselected depth and having a second diameter greater than said first diameter, said second feed conduit having an upper inlet end and a lower discharge end; a supply for supplying refrigerated heat transfer fluid to the inlet ends of said first and second feed conduits for flow therein to the discharge ends of said first and second feed conduits and upwardly through said freeze pipe to freeze the ground adjacent to said bore; and a collection arrangement for collecting the fluid from said freeze pipe.
 2. Apparatus as set forth in claim 1, wherein said first and second feed conduits extend side-by-side in said freeze pipe.
 3. Apparatus as set forth in claim 1, wherein: said freeze pipe has an upper section with a selected diameter and a lower section with a diameter greater than said selected diameter; and said second feed conduit is a dual diameter pipe having said second diameter within the lower section of said freeze pipe and a diameter less than said second diameter within the upper section of said freeze pipe.
 4. Apparatus as set forth in claim 3, wherein: said freeze pipe has a transition between said upper and lower sections thereof, and said discharge end of said first feed conduit is in proximity to said transition.
 5. Apparatus for freezing ground adjacent to a bore, comprising: a first freeze pipe in said bore extending therein from the surface; a first feed conduit extending in said first freeze pipe to a preselected depth and having a first diameter, said first feed conduit having an upper inlet end and a lower discharge end in said first freeze pipe; a second freeze pipe n said bore extending therein from the surface; a second feed conduit extending in said second freeze pipe to a depth greater than said preselected depth and having a second diameter greater than said first diameter, said second feed conduit having an upper inlet end and a lower discharge end in said second freeze pipe; a supply for applying refrigerated heat transfer fluid to the inlet ends of said first and second feed conduits for flow therein to the discharge ends of said first and second feed conduits and upwardly through the respective first and second freeze pipes to freeze the ground adjacent to said bore; and a collection arrangement for collecting the fluid from said first and second freeze pipes.
 6. A method of freezing ground adjacent to a bore extending from the ground surface, comprising: applying refrigerated heat transfer fluid in a first quantity to a first depth in the bore and then upwardly from said first depth to the ground surface for freezing the ground adjacent to the bore from said first depth to the surface; and applying refrigerated heat transfer fluid in a second quantity greater than said first quantity to a second depth in said bore greater than said first depth and then upwardly from said second depth to the ground surface for freezing the ground adjacent to the bore from said second depth to the surface.
 7. A method as set forth in claim 6, wherein: said first and second quantities of fluid are applied through respective first and second feed pipes in the bore; and said second feed pipe has a larger size than said first feed pipe.
 8. A method of freezing ground comprising the steps of: forming a bore into the ground from the surface thereof; applying a first quantity of refrigerated heat transfer fluid to a first depth in the bore and upwardly in the bore to the surface for freezing the ground adjacent to the bore from said first depth to the surface; applying a second quantity of refrigerated heat transfer fluid to a second depth in the bore greater than said first depth and upwardly in the bore to the surface for freezing the ground adjacent to the bore from said second depth to the surface, said second quantity of fluid being greater than said first quantity to compensate for thermal gradients in the ground and enhance uniformity to ground freezing in the depth of the bore.
 9. A method as set forth in claim 8, wherein: said first and second quantities of fluid are applied through respective first and second feed pipes in the bore; and said second feed pipe has a larger size than said first feed pipe. 